No spark 1972 Johnson 100 hp outboard

[tiger 650]

Two weeks ago the engine ran perfect. Last week after pulling the boat on the trailer on a rough dirt road for about a hour the engine would not start after putting it in the water. I checked for spark; there is none. The plugs are clean. The battery is strong because it cranked the motor with no problem. All the electrical connections appear to be solid. I can not see anything that shook loose. What can be wrong?

 

[Joe Reeves]

Re: No spark 1972 Johnson 100 hp outboard

Tiger.... Check the sensor reading with an ohm meter. It should read 4 to 6 ohms (also check the wires for breaks). If this is okay, do the following test.<br /><br />(Battery Capacitance Dischage Powerpack Test)<br />Various OMC Engines - 1968 to 1972)<br /><br />Purchase a small 12v bulb at your local automotive parts store (the 12v bulb is to look like a flashlight bulb, not a headlight bulb). Solder two wires to that bulb, one to the side of the bulb (ground), and the other to the positive point. <br /><br />Remove the spark plugs. With the key in the on position, make sure that you have 12v going to the pack at the terminal block (purple wire). Now, connect the ground wire from the bulb to any powerhead ground. Connect the wire from the positive point of that bulb to the powerpack wire that is connected to the coil wire on the terminal board (blue wire). <br /><br />Crank the engine and observe that bulb closely (CLOSELY!). If that bulb glows even the slightest bit, the powerpack is okay. It may be a very dim glow... just so it glows! If it doesn't glow, the pack has failed. <br /><br />Keep in mind, that type powerpack (Battery Capacitance Discharge) demands a top notch battery of at least 70 amp hours. Any less will, in time, cause powerpack failure.<br /><br />Should the pack prove faulty, I have one new pack left in my remaining stock that I will discount. ReevesJ32@aol.com